Re: [PATCH] mm: add cond_resched() in swapin_walk_pmd_entry()

[Kefeng Wang]

On 2022/12/6 5:03, Andrew Morton wrote:
> On Mon, 5 Dec 2022 22:03:27 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
> > When handle MADV_WILLNEED in madvise(), the soflockup may be occurred
> > in swapin_walk_pmd_entry() if swapin lots of memory on slow device,
> > add a cond_resched() into it to avoid the possible softlockup.
> >
> > ...
> >
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -226,6 +226,7 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
> >   			put_page(page);
> >   	}
> >   	swap_read_unplug(splug);
> > +	cond_resched();
> >   
> >   	return 0;
> >   }
> I wonder if this would be better in walk_pmd_range(), to address other
> very large walk attempts.
mm/madvise.c:287:       walk_page_range(vma->vm_mm, start, end, 
&swapin_walk_ops, vma);
mm/madvise.c:514:       walk_page_range(vma->vm_mm, addr, end, 
&cold_walk_ops, &walk_private);

mm/madvise.c:762:       walk_page_range(vma->vm_mm, range.start, range.end,
mm/madvise.c-763-                       &madvise_free_walk_ops, &tlb);

The cold_walk_ops and madvise_free_walk_ops are already with cond_resched()
in theirs pmd_entry walk, maybe there's no need for a precautionary increase
a cond_resched() for now


> .